1. Field of the Invention
The present invention relates to the field of axial piston machines. It refers to a hydrostatic axial piston machine according to the preamble of claim 1 and to the use of said machine.
2. Description of Related Art
Continuously variable hydrostatic power-branched transmissions, particularly in vehicles used for construction or agricultural purposes, have long been known from the prior art (see, for example, the publications DE-AS-1 113 621, DE-C2-29 04 572, DE-A1-37 07 382, DE-A1-43 43 401 and EP-A1-1 195 542). In these transmissions, the transferred power is apportioned to a mechanical branch and a hydrostatic branch of the transmission as a function of the driving speed, transferred and subsequently combined again.
The hydrostatic power transfer branch of the transmission comprises conventionally two hydrostatic axial piston machines which are connected hydraulically to one another and one of which operates in each case as a pump and the other as a motor. The two machines can in this case interchange their roles, depending on the driving step.
The hydrostatic axial piston machines constitute an essential component of the hydrostatic power-branched transmission and decisively influence the properties of the transmission, such as, for example, the efficiency, the overall size, the complexity, the speed range covered, the type and number of driving steps and the like. Examples of hydrostatic axial piston machines of this type are disclosed in DE-A1-198 33 711 or DE-A1-100 44 784. The functioning and theory of the hydrostatic axial piston machines and a power-branched tractor transmission equipped with them are described in a publication of TU Munich from the year 2000 by H. Bork et al., “Modellbildung, Simulation und Analyse eines stufenlosen leistungsverzweigten Traktor-getriebes” [“Modeling, simulation and analysis of a continuously variable power-branched tractor transmission”].
In the hydrostatic axial piston machines, the cylinder block, into which the axial pistons penetrate, can be pivoted with respect to the driving flange, on which the axial pistons are mounted pivotably, over a pivot angle out of the axially parallel basic configuration. Depending on the pivot angle, in the case of a constant rotational speed, an axial piston machine operating as a pump conveys more or less volume per unit time. In an axial piston machine operating as a motor, the pivot angle influences the torque output and the rotational speed. Owing to the cooperation of two axial piston machines operating as a pump and as a motor in a power-branched transmission, the driving speed can be set independently of the engine rotational speed of the driving internal combustion engine, in that the pivot angles of the pump and motor are suitably varied. Thus, in a tractor, it is possible, for example, in spite of a changing driving speed, to keep the rotational speed of the diesel engine constant and to operate the engine at the most beneficial operating point, or to adapt the rotational speed of the take-off shaft optimally to the work task of the accessory driven by means of the take-off shaft.
The maximum possible pivot angle of the axial piston machine determines the operating range of the axial piston machine and therefore also the properties of the transmission. In axial piston machines known hitherto, the maximum pivot angle is restricted to values equal to or lower than 45°. This leads to a restriction in power and in the range of variation. The result of this, too, is that the power-branched transmissions in which the axial piston machines are used are restricted in efficiency, cover a restricted speed range per driving step and entail a comparatively high outlay in terms of construction and space requirement.
The object of the invention, therefore, is to provide a hydrostatic axial piston machine which is distinguished by markedly improved properties, as compared with the known axial piston machines, and, when used in a power-branched transmission, leads to corresponding improvements in the transmission properties.